I've been playing on a server I have running on one of my computers for a few days now. I got a friend to join in recently, and the last time I tried to connect to play with him I lost all of my previous progress. Any idea how I could recover this or fix this from happening in the future?

This could've been the bug where your progress was not saved when you left the server. The bug should be fixed as of 6192598.
If it wasn't fixed, re-open this issue.

Closed #197.

After having it happen a second time, I changed my approach. I now save my game using a unique name rather than the default "quicksave". My guess is that the server shares these resources with all players in the server. If someone new joins and saves to quicksave, then all "quicksaves" are overwritten. Since I started using unique names, I haven't ran into the issue since. This is all speculative by the way.

This just happened to me as well.

I played, friend joined, I played, Friend did 3-4 play sessions. When I logged back on I was reset to starting.

My server is set up for career mode by the way.